1. Field of the Invention
The present invention relates to a probe to be used for scanning probe microscopes, the manufacturing method thereof, and an information processing device using the probe.
2. Related Background Art
There are surface microscopes having space resolution on an atomic scale in practical use such as scanning tunneling microscopes (hereafter referred to as "STM") and scanning atomic force microscopes (hereafter referred to as "AFM"), such surface microscopes being collectively referred to as scanning probe microscopes (hereafter referred to as "SPM").
Regarding such SPMs, an information recording/reproducing device which writes recording information to a local area is being considered, making application of the fact that the tip is capable of accessing the surface of a sample at the atomic level.
With the STM, a tunnel current is detected between a biased electroconductive tip and an electroconductive sample with the distance therebetween being within several Angstroms, the tip is scanned while the distance between the tip and sample is controlled so as to be maintained at a constant in order to make the tunneling current constant, and a surface image is formed by imaging the tunnel current or feedback control signals. Examples of recording methods applying the STM include a method wherein electric voltage is applied between the tip and recording medium and a change in format of the surface of the recording medium is brought about locally, or a method wherein the electroconductivity of the recording medium is changed.
On the other hand AFMs detect the atomic force operating upon the tip and sample surface at the time that the tip is brought within several Angstroms of the sample, and the tip is scanned in two-dimensional planar fashion, thus obtaining a surface image including three-dimensional information.
As for the means for detecting atomic force, an elastic lever of which one end is fixed and the tip is held near the free end is employed.
As for a multi-functional microscope for making AFM and STM observation with a single apparatus, there is a multiplex atomic force microscope/scanning tunneling microscope (AFM/STM).
According to this arrangement, the probe used for the AFM is comprised of a cantilever and a tip held by the cantilever, detecting the current between the tip and sample by making the tip to be electroconductive.
With a normal method of usage, bias is applied between the tip and sample at the time that the AFM is operating and the current is detected, thereby obtaining a three-dimensional surface image and tunneling current distribution image simultaneously with a single tip.
Regarding this multiplex apparatus as well, an information recording/reproducing device which writes recording information to a local area is being considered, making application of the fact that the tip is capable of accessing the surface of a sample at the atomic level. In such a case, a plurality of probes are used in order to increase the writing or reading speed (Japanese Patent Application Laid-Open No. 4-321955).
The conventional method for manufacturing probes (U.S. Pat. No. 5,221,415) involves first performing anisotropic etching by crystal axis of a mono-crystalline Si substrate 402 upon which a Si dioxide layer 401 has been formed as shown in FIGS. 1A to 1G, forming an inverse pyramid recess 403 (FIG. 1A).
After forming the recess 403, the Si dioxide layer 401 is removed. While this recess 403 is used as a mold for the tip, the entire surface is then coated with a silicon nitride layer 404 (FIG. 1B), patterning is performed in the form of the cantilever 405 (FIG. 1C), a glass plate 408 provided with a saw-cut groove 406 and Cr layer 407 is brought into contact with the silicon nitride layer 404 (FIG. 1D), part of the glass plate 408 is ruptured so as to form a mounting block 408a (FIG. 1E), and the mono-crystalline Si substrate 402 is etched away to obtain a cantilever-shaped probe 409 (FIG. 1F). Finally, a metal layer 410 which serves as the reflecting film for the optical lever type AFM is formed (FIG. 1G).
Also, regarding the method of forming the tip, there are a method such as shown in FIG. 2A wherein a thin-film layer is patterned on the substrate in the form of a circle, which is used as a mask for etching the Si substrate 502, thereby obtaining a tip 503 by side-etching (O. Wolter, et. al, "Micromachined silicon sensors for scanning force microscopy", J. Vac. Sci. Technol. B9(2) Mar/Apr, 1991, pp 1353-1357), a method wherein as shown in FIG. 2B a reverse-tapered opening 504a is formed in resist 504 and vapor-deposition of electroconductive material 505 is performed thereto from an angle while rotating the substrate 506, thereby forming a tip 503 by lifting off (C. A. Spindt, et. al., "Physical properties of thin film field-emission cathode with molybdenum cones", J. Appl. Phys., 47. 1976, pp 5248-5263), and so forth.
However, the examples shown in FIGS. 1A to 1G and 2A and 2B have the following problems:
First, regarding the lever:
Film of SiO.sub.2, SiN, SiC, C, etc., formed by vacuum deposition or CVD are polycrystalline or amorphous, and have internal stress to a certain extent, resulting in the problem of the lever itself bowing. PA1 In the case that a portion of a thin-film lever of material such as SiO.sub.2 or SiN is held by a thick substrate such as a Si substrate, stress is generated at the layered portions thereof, and this stress is particularly centralized on the base portion where the lever is attached, so repeated operation of the lever can lead to destruction from that portion. PA1 In the event that the cantilever-shaped probe is coated with metal film or the like to provide it with light-reflecting or electroconductive properties, such a phenomenon occurs that stress is generated between the cantilever and metal film, causing the cantilever to bow. PA1 In the event that the cantilever bows toward the tip, or in the event that the tip of the cantilever bows in the reverse, the center of the cantilever may come into contact with the sample or recording medium. PA1 Further, in the event that a plurality of probes are used, a particular problem is irregularity in the bowing thereof. That is, in the event of using an information processing device using the AFM/STM principles, when a plurality of probes on a single plane are to be brought into simultaneous contact with a recording medium, the load of each probe on the recording medium differs if there is irregularities in the levers, causing problems such as deterioration of resolution or destruction of the recording medium or tip, depending on the load. PA1 In the case that a cantilever-shaped probe is coated with electroconductive material to form an STM probe, the pointed end of the tip is not easily coated due to the sharp form thereof, and it is difficult to obtain stable properties with STM which handles tunneling current which is a very weak current. PA1 With such tips shown in FIG. 2A and FIG. 2B, it is difficult to make constant the resist patterning conditions or the material etching conditions at the time of forming the tip, meaning that it is difficult to accurately maintain the form of the plurality of tips being formed, i.e., the height and end curvature radius thereof, and the tip becomes heavy due to being formed completely of metal, thus exhibiting a problem of decrease in resonance frequency.
Also, regarding the tip: